SE2050727A1 - Methods of navigating a self-propelled robotic tool, and robotic tools, and computer pograms implementing such methods - Google Patents

Abstract

A method of navigating a self-propelled robotic tool (14) to perform a task within a work area comprises planning a route to cover the work area with a work implement (44), with an operating width overlap (OL) between adjacent paths (P1, P2), to obtain a present planned route (RP); navigating the work area according to the present planned route (RP) while performing the task; determining an estimated actual route based on positioning information from a positioning device (34); estimating a deviation of the estimated actual route from the present planned route (RP); and setting an updated operating width overlap (OL) based on the estimated deviation of the estimated actual route from the present planned route (RP).

Description

METHODS OF NAVIGATING A SELF-PROPELLED ROBOTIC TOOL, ANDROBOTIC TOOLS AND COMPUTER PROGRAMS IMPLEMENTING SUCHMETHODS Field of the inventionThe present invention relates to methods of navigating a robotic tool, forexample a robotic Iawnmower, within a work area.

BackgroundSelf-propelled robotic tools are widely used to perform maintenance operations within a predetermined work area. By way of example, roboticIawnmowers are used for autonomously cutting Iawns within a predetermined workarea to be mowed. The size of the area that can be serviced by a robotic Iawnmowermay be limited by various considerations, such as battery capacity (for electricallypowered Iawnmowers), work area complexity, and the ability to navigate the workarea in a systematic manner. There is a strive for increasing the area capacity ofrobotic Iawnmowers. Other exemplary considerations in Iawnmower design are cost,complexity, reliability, visual cutting result, and ease of use.

US 2015/0234385 A1 discloses a systematic navigation method according towhich a Iawnmower navigates within boundaries defining an area to be mowed, anduses grass length sensors to follow an edge between cut grass and un-cut grass.

Summafllt is an object of the present invention to solve, or at least mitigate, parts or all of the above mentioned problems. To this end, according to a first aspect, there isprovided a method of navigating a self-propelled robotic tool to perform a task withina work area, the robotic tool comprising a positioning device and a work implementhaving an operating width, the method comprising planning a route to cover the workarea with the work implement, with an operating width overlap between adjacentpaths, to obtain a present planned route; navigating the work area according to thepresent planned route while performing the task; determining an estimated actualroute based on positioning information from the positioning device; estimating adeviation of the estimated actual route from the present planned route; and setting anupdated operating width overlap based on the estimated deviation of the estimatedactual route from the present planned route. Thereby, the operating width overlapmay be precisely adapted to the actual navigation or traction conditions of the work 1 area, such that excess overlap may be avoided. This allows shortening the timerequired to perform the task, and/or expanding the work area that can be processedby the robotic tool. lt may also reduce energy consumption of the robotic tool, and thewear on the robotic tool as well as on the work area. For example, slopes, roughwork area surface, obstacles, and/or other difficult terrain may move the robotic toolout of its planned route. Such deviations may be compensated for by adjusting theoperating width overlap. Typically, the task may be of such a character that the entirework area should be covered or processed by the route of the robotic tool. Thepresent planned route for covering the work area may be determined prior tonavigating the work area. The work area may be defined on a map stored in amemory of the robotic tool. A route plan may extend across the work area in such amanner that substantially the entire work area will be covered by the robotic tool, i.e.overrun within the operating width of the working implement of the robotic tool.

According to embodiments, setting an operating width overlap based on theestimated deviation of the estimated actual route from the present planned route maycomprise setting the operating width overlap for a next planned route.

According to embodiments, setting an operating width overlap based on theestimated deviation of the estimated actual route from the present planned route maycomprise setting the operating width overlap for the present planned route; and re-planning the present planned route.

According to embodiments, estimating a deviation of the estimated actualroute from the present planned route may comprise estimating a local deviation of anactual position, determined based on positioning information from the positioningdevice, from a planned position according to the present planned route; and setting alocal operating width overlap for a next planned route based on the estimated localdeviation of the actual position from the planned position.

According to embodiments, estimating a deviation of the estimated actualroute from the present planned route may comprise estimating an average deviationof the estimated actual route from the present planned route.

According to embodiments, estimating a deviation of the estimated actualroute from the present planned route may comprise estimating a maximum deviationof the estimated actual route from the present planned route.

According to embodiments, planning a route to cover the work area with thework implement, with an operating width overlap between adjacent paths, to obtain apresent planned route, may comprise setting the operating width overlap based on 2 terrain information in a stored map. The operating width overlap may be set to thesame value for the entire route. Alternatively, different positions or route segmentsalong the route may be given different local operating width overlap settings basedon the local terrain indicated on the map. Terrain information used for setting theoperating width overlap may comprise e.g. slope inclination, GNSS shadowing,and/or drive wheel grip/traction conditions.

According to embodiments, the present planned route may comprise said atleast a portion of the work area being covered by a set of parallel paths oriented in afirst direction.

According to embodiments, the method may further comprise comparing thedeviation of the estimated actual route from the present planned route to a previouslystored deviation of a previous estimated actual route from a previous route plan, theprevious route plan being different from the present route plan; and setting a nextroute based on said comparison.

According to embodiments, the previous route plan may comprise said at leasta portion of the work area being covered by a set of parallel paths oriented in asecond direction different from said first direction. By trying different orientations of asystematic pattern in the same work area, the orientation requiring the least overlapmay be found. For example, the deviations between actual and planned routes maydiffer quite a lot depending on whether a slope is navigated straight uphill/downhill orleaning sideways.

According to embodiments, planning a route may comprise defining a route ina GNSS (Global Navigation Satellite System) reference system, and navigating thework area may comprise receiving GNSS signals. The GNSS signals may bereceived exclusively from satellites, or may be supplemented by signals from one orseveral local positioning beacons. By way of example, the robotic tool may beconfigured to determine its position using RTK- (Real-Time Kinematic) enhancedGNSS to obtain high positioning accuracy.

According to embodiments, the updated operating width overlap may furtherbe based on an estimated accuracy of positioning information from the positioningdevice.

According to embodiments, the work implement may have a fixed operatingwidth, and setting an operating width overlap may comprise setting a centre-to-centredistance between adjacent paths. Alternatively, the work implement may have an adjustable operating width, and the robotic tool may be configured to automaticallyadjust the operating width based on the estimated deviation.

According to embodiments, the robotic tool may be a robotic garden tool. Therobotic garden tool may be a robotic lawnmower, the work implement may be a grasscutter, the operating width may be a cutting width, and the task may be cutting grass.

According to a second aspect, parts or all of the above mentioned problemsare solved, or at least mitigated, by a method of navigating a self-propelled robotictool to perform a task within a work area, the method comprising navigating the workarea according to a present route plan while performing the task; recording anestimated actual route based on positioning information from a positioning device;estimating a deviation of the estimated actual route from the route plan; comparingthe estimated deviation to a previously stored estimated deviation from a previousroute plan, the previous route plan being different from the present route plan; andsetting a next route plan based on said comparison. Thereby, previous routes whichcause less deviation between the actual and planned routes may be automaticallypreferred. Typically, the route plan resulting in the lowest deviations may bepreferred. An operating width overlap for the next route plan may be set based on anexpected deviation of the estimated actual route from the selected next route plan.The expected deviation may be based on deviations estimated during one or severalprevious runs of a route plan corresponding to the selected route plan. Again, therobotic tool may be a robotic garden tool such as a robotic lawnmower. The methodand the robotic tool may be configured in accordance with any of the embodimentsdefined above.

According to a third aspect, parts or all of the above mentioned problems aresolved, or at least mitigated, by a method of navigating a self-propelled robotic tool toperform a task within a work area, the robotic tool comprising a positioning deviceand a work implement having an operating width, the method comprising planning aroute to cover the work area with the work implement, with an operating widthoverlap between adjacent paths, to obtain a present planned route; navigating thework area according to the present planned route while performing the task;determining an estimated actual route based on positioning information from thepositioning device; estimating, for a path, a deviation of the estimated actual routefrom the present planned route; based on the deviation, determining that the path is afailed path; and updating the present planned route with at least one supplementarypath adjacent to the failed path. Thereby, the robotic tool may ascertain that a 4 sufficient area coverage is obtained. According to embodiments, a supplementarypath may be added adjacent to the failed path on each side of the failed path.

According to a fourth aspect, parts or all of the above mentioned problems aresolved, or at least mitigated, by a self-propelled robotic tool comprising a positioningdevice, a work implement configured to carry out a task in a work area, andprocessing equipment configured to carry out any of the methods defined above.

According to a fifth aspect, parts or all of the above mentioned problems aresolved, or at least mitigated, by a computer program product comprising instructionswhich, when the program is executed on a processor, carries out any of the methodsdefined above.

According to a sixth aspect, parts or all of the above mentioned problems aresolved, or at least mitigated, by a computer-readable medium comprising executablecode representing instructions to a self-propelled robotic tool to perform any of themethods defined above. lt is noted that embodiments of the invention may be embodied by all possiblecombinations of features recited in the claims. Further, it will be appreciated that thevarious embodiments described for the method according to the first aspect arecombinable with the methods according to the second and third aspects, as well aswith the device according to the fourth aspect and the computer programs of the fifthand sixth aspects, and vice versa.

Brief description of the drawinqs The above, as well as additional objects, features and advantages of thepresent invention will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, withreference to the appended drawings, where the same reference numerals and letterswill be used for similar elements, wherein: Fig. 1 is a perspective view of a robotic lawnmower system comprising acharging station and a robotic lawnmower servicing a work area; Fig. 2 is a block diagram of the robotic lawnmower of Fig. 1, and illustrates various functional blocks of the robotic lawnmower; Fig. 3 is a perspective view of a cutting device of the robotic lawnmower of Fig. 1;Fig. 4 is a schematic illustration of path segments of an exemplary navigationroute, as seen from above, of the robotic lawnmower of Fig. 1; Fig. 5 is a schematic illustration of a path segment of a planned navigationroute, along with a corresponding segment of an actual navigation route, as seenfrom above; Fig. 6 is a schematic illustration of a planned navigation route, as seen fromabove, of the robotic lawnmower of Fig. 1, for covering a work area during a worksession; Fig. 7 is a schematic illustration of another planned navigation route, as seenfrom above, of the robotic lawnmower of Fig. 1, for covering the work area duringanother work session; Fig. 8 is a flow chart illustrating a first method of planning a route of the roboticlawnmower of Fig. 1; Fig. 9 is a flow chart illustrating a second method of planning a route of therobotic lawnmower of Fig. 1; Fig. 10 is a flow chart illustrating a third method of planning a route of therobotic lawnmower of Fig. 1; and Fig. 11 is a perspective view of a storage medium carrying a computerprogram implementing any of the methods of Figs 8-10.

All the figures are schematic, not necessarily to scale, and generally only showparts which are necessary in order to elucidate the embodiments, wherein other partsmay be omitted.

Detailed description of the exemplarv embodimentsFig. 1 schematically illustrates an overview of a robotic tool system 10 configured to perform a task within a work area 12 such as a garden, a parcel, a cropfield, or a floor area. The robotic tool system 10 comprises a battery-powered, self-propelled, and autonomously navigating robotic tool 14, along with a charging station16 for charging a battery of the robotic tool 14. As primarily described herein, therobotic tool 14 may be a robotic lawnmower, and for the sake of simplicity, it will bereferred to as such in the following. However, the present disclosure may also beuseful in connection with self-propelled robotic tools configured as golf ball collectingtools, vacuum cleaners, floor cleaners, street sweepers, snow removal tools,agricultural machinery, mine clearance robots, or any other type of robotic tool that isrequired to operate over a work area in a methodical and systematic or positionoriented manner. ln particular, the teachings herein may be of particular use inrobotic tools configured to execute a task over an area to be treated, wherein a full or 6 at least predetermined coverage of the area to be treated is desired. The work area12 may be delimited by a boundary 13 which may be physical, i.e. defined byphysical obstacles or a boundary cable carrying a boundary signal, or virtual, i.e.based on positions of boundary segments in a map used by the robotic lawnmower14 for navigating.

The robotic lawnmower 14 is provided with wheels 18, 20 for moving within thework area 12. ln the illustrated example, the robotic lawnmower 14 has two frontwheels 18, which are of caster type, and two rear wheels 20, even though only one ofeach wheel type 18, 20 is visible in the view of Fig. 1. Typically, at least one of thewheels 18, 20 is connected to a motor, such an electric motor, either directly or via atransmission (not illustrated), for propelling the robotic lawnmower 14. A robotic toolalso typically comprises at least one work implement configured to perform the taskon the area to be treated. ln the example of the robotic lawnmower 14, the workimplement is a grass cutter (not illustrated), which may be rotatable about a verticalaxis.

Fig. 2 illustrates functional blocks of the robotic lawnmower 14. ln the exampleof Fig. 2, each of the rear wheels 20 is connected to a respective electric propulsionmotor 24. This allows for driving the rear wheels 20 independently of one another,enabling e.g. steep turning of the robotic lawnmower 14. The robotic lawnmower 14further comprises a controller 26. The controller 26 may be connected to sensors,actuators, and communication interfaces of various kinds, and may be implementedusing central processing unit executing instructions stored on a memory 28.Needless to say, different combinations of general and application-specific integratedcircuits may be used for the controller 26. Similarly, the memory 28 may beimplemented using many different memory technologies. ln general, the controller 26is configured to read instructions from the memory 28 and execute these instructionspossibly in view of different sensor signals to control the operation of the roboticlawnmower 14. Typically, the controller 26 is configured to, based on the instructions,control the robotic lawnmower in an autonomous or semi-autonomous manner, i,e.with no, or only occasional, instructions from a human operator. The controller 26also controls the operation of a cutter motor 30, which is configured to drive the grasscutter.

A wireless transceiver 32 is connected to the controller 26, and allows thecontroller 26 to communicate with the charging station 16 or any other device, such as a remote control or a smart phone (not shown).7 The robotic lawnmower 14 further comprises a positioning device 34. ln theillustrated example, the positioning device 34 comprises an inertial navigation device36, such as an accelerometer or a gyroscope, which allows the robotic lawnmower14 to keep track of its movement within the area 12 to be treated. The inertialnavigation device 36 may be supplemented by a compass 38, to provide basicorientation information that may compensate for any drift of the inertial navigationdevice 36. The positioning device 34 further comprises a GNSS (Global NavigationSatellite System) receiver 40, which may receive navigation signal from navigationsatellite systems such as GPS (Giobai Positioning System) satoliites, GLGNASSsateliites, Beidou sateiiites, Gaiileo sateiiites, or any combination of those. TheGNSS satellite signals may be supplemented by correction signals from one orseveral local beacons, or over a network, which may enable RTK (real-timekinematic) enhanced GNSS navigation. A local RTK beacon may e.g. be arranged inthe charging station 16 (Fig. 1).

The controller 26 also controls the propulsion motors 24, thereby controllingthe propulsion of the robotic lawnmower 14 within the area 12 to be treated. Thepropulsion motors 24 may be stepper motors, allowing the controller 26 to keep trackof the respective number of turns of the motors 24, and thereby also the distancetravelled by the robotic lawnmower 14, as well as any turning angle of the roboticlawnmower 14 when the motors 24 are operated at different speeds or in reversedirections. ln this respect, the propulsion motors 24 operate as odometers.Alternatively, the wheels 20 may be provided with odometer indexers configured toprovide feedback to the controller 26 about the number of turns of each motor 24.

Navigation information from the positioning device 34 and the motors 24 isfused in the controller 26 to provide an accurate position indication, in order to enablean accurate and systematic movement pattern of the robotic lawnmower 14 forcovering the work area 12 (Fig. 1). Typically, high-precision positioning using e.g.RTK GNSS also allows obtaining an estimate of the current accuracy of the obtainedposition. The controller 26, positioning device 34, transceiver 32, and electric motors24, 30 are powered by a battery 42. The robotic lawnmower 14 is configured tonavigate to the charging station 16 (Fig. 1) on a regular basis, for example betweenwork sessions and/or whenever the battery charge is running low, in order to dockwith the charging station 16 for recharging the battery 42. The charging station 16may be connected so as to receive power from the electric power grid.

Fig. 3 illustrates an exemplary grass cutter 44 as seen obliquely from below.The grass cutter 44 comprises a plurality of grass cutting blades 46, which arepivotally connected to the radial periphery of a knife carrier disc 48. The knife carrierdisc 48 is configured to be rotated about a substantially vertical cutter axis C by thecutter motor 30. A skid plate 50 is positioned below the knife carrier disc 48; the skidplate 50 is rotatable in relation to the knife carrier disc 48 about the cutter axis C,such that the skid plate 50 may remain non-rotary in relation to the grass to be cut,while the knife carrier disc 48 rotates.

Referring back to Fig. 1, the robotic lawnmower 14 stores in its memory 28(Fig. 2) a map of the work area 12, and is configured to navigate the work area 12 ina systematic manner. For optimum coverage, the robotic lawnmower 14 plans itsroute within the work area 12 to follow parallel, adjacent paths. As the roboticlawnmower 14 propels itself forward while cutting grass, the grass cutter 44 (Fig. 3)cuts within a cutting width, which is determined by the diameter of the trajectory ofthe cutting blades' 46 radially outermost tips about the cutting axis C. This brings usto Fig. 4, which illustrates a segment of a route plan RP to be followed by the roboticlawnmower 14, along with two positions of the robotic lawnmower 14 along the routeplan RP, at two different times during a work session. The route plan RP comprisesadjacent, straight, parallel path segments P1, P2. which are separated by a centre-to-centre separation distance S. The cutting width W of the grass cutter 44 (Fig. 4)results in a cutting overlap OL of the adjacent parallel path segments P1, P2. Thecontroller 26 (Fig. 2) plans the route RP to obtain an overlap OL which is sufficient forcovering a typical lawn. The route plan RP may account for known terrain conditionsand positioning accuracies at different positions of the stored map, and the overlapOL may be set differently at different positions. For example, the controller 26 mayplan the route RP to have more closely spaced paths P1, P2 in areas where theterrain is sloping sideways, relative to the robotic lawnmower's 14 heading, toincrease the overlap OL where the robotic lawnmower 14 may be expected to slipsideways.

Once having a route plan RP for at least a portion of the work area 12, therobotic lawnmower 14 will navigate according to the planned route RP, based onpositioning information from the positioning device 34 (Fig. 2), while cutting grass.While doing so, the robotic lawnmower 14 may face varying conditions that make therobotic lawnmower 14 deviate from the planned route RP.

Fig. 5 illustrates a segment of the planned route RP along with an exemplaryestimated actual route RA. The estimated actual route RA may be estimated by thecontroller 26 based on position information from the positioning device 34 (Fig. 2).For example, when the centre of the robotic lawnmower 14 according to the presentroute plan RP should be at a planned position PP along the planned route RP, it mayactually be at an actual position PA, which may be displaced from the planned routeRP by a deviation D. When navigating the work area 12 (Fig. 1), the roboticlawnmower 14 continuously or regularly estimates the deviation D based onestimated positions received from the positioning device 34. The estimated deviationD represents the shortest distance from an estimated actual position PA to theplanned route RP. Hence, the deviation D may vary along the actual route RA of therobotic lawnmower 14. The estimated deviation D may also incorporate an estimatedpositioning error determined by the positioning device 34, by adding the uncertaintyof the estimated position to the estimated distance between the estimated actualposition PA and the planned route RP. The robotic lawnmower 14 may furtherdetermine, for a route segment or for the entire planned route RP, an averageestimated deviation DA, as well as a maximum estimated deviation DM. All thosevalues D, DA, DM represent different measures of a deviation between the actualroute RA and the planned route RP. lf the deviation, as represented e.g. by any of the values D, DA, DM, is greaterthan what may be typical, the robotic lawnmower 14 may increase the operatingwidth overlap OL (Fig. 4) for the next work session to avoid leaving strips of uncutgrass between adjacent path segments P1, P2 (Fig. 4). This may be done bygenerating an updated route plan with more closely spaced adjacent path segmentsP1, P2. Similarly, if the deviation is smaller than what may be typical, the roboticlawnmower 14 may generate an updated route plan with an increased separationdistance S (Fig. 4), i.e. smaller overlap OL (Fig. 4), to enable covering the work areawith fewer parallel paths P1, P2. The separation distance S should typically not beallowed to exceed the cutting width W (Fig. 4). The robotic lawnmower 14 may iteratethe procedure, i.e. for each time a route plan RP is pursued, deviations from therespective route plan RP are estimated, and an updated overlap is generated for thenext route plan. lt may also be beneficial to limit the magnitude of the overlap changefor each iteration, in order to trigger slow overlap changes over time, therebyaccommodating for temporary variations of traction conditions.

Fig. 6 illustrates an exemplary work area 12 within a boundary 13, along withan exemplary route plan RP. The route plan RP may comprise a route segment Bfollowing the contour of the boundary 13, for cutting the outer edge of the work area12, and a plurality of parallel path segments P1, P2 etc., which are mutually spacedto generate an overlap OL in the manner illustrated in Fig. 4. The work area may belocated on a slope, indicated by a direction of downhill inclination i. The plurality ofparallel path segments P1, P2 are oriented in a first direction, which in the illustratedexample coincides with the direction of the slope's inclination i. After having pursuedthe route plan RP, the controller 26 (Fig. 2) may evaluate the estimated deviationbetween actual and planned routes RA (Fig. 5), RP, and set an updated overlap OL(Fig. 4) for the next route plan to position some or all of the parallel paths P1, P2closer or further away from each other. Alternatively or additionally, the controller 26may also set an updated overlap OL for remaining parts of the present route plan RPprior to finishing the present work session, and re-plan the remainder of the presentroute plan RP. The parallel paths of the next route plan may be directed in the samedirection as the paths P1, P2 of the present route plan RP.

Fig. 7 illustrates an exemplary alternative next route plan RP2 for the samework area 12, according to which the parallel paths are oriented differently. Based onlocal differences of the estimated deviation D from the route plan RP of Fig. 6,different overlaps OL (Fig. 4) may be set for different positions or sub-areas of thework area 12, or for different path segments along the next planned route RP2.Similar to the route plan of Fig. 6, also the next route plan RP2 may comprise a routesegment B following the contour of the boundary 13, and a plurality of parallel pathsegments P3, P4. The separation distances between the path segments P3, P4 ofthe next route plan RP2 may, based on any changes to the overlap OL (Fig. 4), bedifferent from the separation distances between the path segments P1, P2 of Fig. 6.The robotic lawnmower 14 may also try a different orientation of the parallel pathsegments; in the example illustrated in Fig. 7, the parallel path segments P3, P4 areoriented perpendicular to the direction of the slope inclination i. Once the roboticlawnmower 14 has planned the next route RP2, the next route plan RP2 becomesthe present planned route RP to be pursued, and the procedure may be iterated. Foreach orientation that the robotic lawnmower 14 tries, different local, average, and/ormaximum deviations D, DA, DM may be obtained, for example due to the roboticlawnmower 14 propelling itself along differently oriented parallel path segments inrelation to the direction of the slope inclination i. The controller 26 (Fig. 2) may also 11 select, for a next planned route RP2, a previously pursued route plan RPO thatoptimizes any selected measure of the deviation D, DA, DM. For example, the roboticlawnmower 14 may test several different route plans during a running-in period, andfor each new route plan it tries, the robotic lawnmower may compare the averagedeviation DA with average deviations of previously tried routes, and keep track ofwhich route gives the least average deviation. ln the illustrated example of Fig. 7, thenext planned route RP2 may e.g. be a copy of a previously pursued route plan RPO,the pursuing of which has been tested to result in a minimum of average deviationDA of the actual route from the respective planned route RPO. Alternatively, apreviously pursued route plan RPO, which has yielded good deviation results, may beslightly modified before setting as the next route plan RP2 in a manner similar to agenetic algorithm.

Now returning to the situation of Fig. 6, the controller 26 may compare theestimated deviation D, DA, DM to the overlap OL according to the planned route RP,and based on the comparison, determine that that a path, for example the path P1,was failed in the sense that the overlap was insufficient to accommodate for thedeviation from the planned route RP. lt can therefore be expected that strips of uncutgrass remain on one or both sides of the failed path P1. ln response thereto, thecontroller may update the present planned route RP with a pair of supplementarypaths P1', P1" straddling the failed path P1.

Referring back to Fig. 5, it may also happen that an actual route RA deviatessubstantially from the planned route RP only at a specific location, but otherwiseremains close to the planned route RP. ln such a situation, it may be assumed thatthe large deviation may result from e.g. obstacles along the route, and the local, largedeviation may therefore be disregarded when setting the overlap OL for the nextplanned route.

The flow chart of Fig. 8 illustrates a method according to which the roboticlawnmower 14 of Fig. 1 dynamically adapts its cutting width overlap OL. ln step 801, the robotic lawnmower 14 plans a route to cover the work area 12with the cutter 44, with an operating width overlap OL between adjacent paths (P1,P2 (Fig. 6), to obtain a present planned route RP. ln step 802, the robotic lawnmower 14 navigates the work area 12 accordingto the present planned route RP while cutting grass, and while determining anestimated actual route RA (Fig. 5) based on positioning information from thepositioning device 34 (Fig. 2). 12 ln step 803, the robotic lawnmower 14 estimates a deviation DA (Fig. 5) of theestimated actual route RA from the present planned route RP. ln step 804, the robotic lawnmower 14 sets an updated operating widthoverlap OL based on the estimated deviation DA of the estimated actual route RAfrom the present planned route RP.

The flow chart of Fig. 9 i||ustrates a method according to which the roboticlawnmower 14 of Fig. 1 evaluates previous route plans, and plans future routesbased on the evaluations. ln step 901, the robotic lawnmower 14 navigates the work area 12 accordingto a present route plan RP (Fig. 6) while cutting grass, and while recording anestimated actual route RA (Fig. 5) based on positioning information from apositioning device 34 (Fig. 2). ln step 902, the robotic lawnmower 14 estimates a deviation DA (Fig. 5) of theestimated actual route RA from the route plan RP. ln step 903, the robotic lawnmower 14 compares the deviation DA to apreviously stored deviation from a previous route plan, the previous route plan beingdifferent from the present route plan RP. ln step 904, the robotic lawnmower 14 sets a next route plan RP2 (Fig. 7)based on the comparison in step 903.

The flow chart of Fig. 10 i||ustrates a method according to which the roboticlawnmower 14 of Fig. 1 detects failed paths and inserts supplementary paths. ln step 1001, the robotic lawnmower 14 plans a route to cover the work area12 with the grass cutter 44, with an operating width overlap OL (Fig. 4) betweenadjacent paths P1, P2 (Fig. 4), to obtain a present planned route RP. ln step 1002, the robotic lawnmower 14 navigates the work area 12 accordingto the present planned route RP while cutting grass and while determining anestimated actual route RA (Fig. 5) based on positioning information from thepositioning device 34 (Fig. 2). ln step 1003, the robotic lawnmower 14 estimates, for a path P1 (Fig. 6), adeviation D (Fig. 5) of the estimated actual route RA from the present planned routeRP, and determines, based on the deviation D, that the path P1 is a failed path. ln step 1004, the robotic lawnmower 14 updates the present planned route RPwith a pair of supplementary paths P1', P1" (Fig. 6) adjacent to the failed path P1.

The methods described herein may be implemented in a computer program,which may be loaded or loadable into the controller 26 for execution. The computer 13 program may be carried by a computer readable medium, such as compact disc,flash memory, or similar device in any manner apparent to those skilled in the art.Fig. 12 illustrates an exemplary portable memory, in the embodiment of a compactdisc 98, carrying such a computer program. The compact disc 98 is loadable into acomputer (not illustrated) connectable to the robotic Iawnmower 14, for transfer of theprogram to the robotic Iawnmower 14.

The invention has mainly been described above with reference to a fewembodiments. However, as is readily appreciated by a person skilled in the art, otherembodiments than the ones disclosed above are equally possible within the scope ofthe invention, as defined by the appended patent claims. For example, deviationsmay be represented not only by its local, average, and maximum values; also otherdeviation measures indicating how well a robotic tool follows a planned route may beused. ln the claims, the word "comprising" does not exclude other elements or steps,and the indefinite article "a" or "an" does not exclude a plurality. 14

Claims (17)

A method of navigating a self-propelled robotic tool (14) to perform a taskwithin a work area (12), the robotic tool (14) comprising a positioning device(34) and a work implement (44) having an operating width (W), the methodcomprising planning a route to cover the work area (12) with the work implement(44), with an operating width overlap (OL) between adjacent paths (P1, P2), toobtain a present planned route (RP); navigating the work area (12) according to the present planned route(RP) while performing the task; determining an estimated actual route (RA) based on positioninginformation from the positioning device (34); estimating a deviation (D; DA; DM) of the estimated actual route (RA)from the present planned route (RP); and setting an updated operating width overlap (OL) based on the estimateddeviation (D; DA; DM) of the estimated actual route (RA) from the presentplanned route (RP).

1. The method according to claim 1, wherein setting an operating width overlap

2. (OL) based on the estimated deviation (D; DA; DM) of the estimated actualroute (RA) from the present planned route (RP) comprising setting theoperating width overlap (OL) for a next planned route (RP2).

3. The method according to any of the preceding claims, wherein setting anoperating width overlap (OL) based on the estimated deviation (D; DA; DM) ofthe estimated actual route (RA) from the present planned route (RP)comprises setting the operating width overlap (OL) for the present planned route(RP); and re-planning the present planned route (RP).

4. The method according to any of the preceding claims, wherein estimating a deviation (D; DA; DM) of the estimated actual route (RA)from the present planned route (RP) comprises estimating a local deviation (D)of an actual position (PA), determined based on positioning information from the positioning device (34), from a planned position (PP) according to thepresent planned route (RP); and setting a local operating width overlap (OL) for a next planned route (RP)based on the estimated local deviation (D; DA; DM) of the actual position (PA)from the planned position (PP).

5. The method according to any of the preceding claims, wherein estimating a deviation (D; DA; DM) of the estimated actual route (RA) from the presentplanned route (RP) comprises estimating an average deviation (DA) of theestimated actual route (RA) from the present planned route (RP).

6. The method according to any of the preceding claims, wherein estimating a deviation (D; DA; DM) of the estimated actual route (RA) from the presentplanned route (RP) comprises estimating a maximum deviation (DM) of theestimated actual route (RA) from the present planned route (RP).

7. The method according to any of the preceding claims, wherein planning a route to cover the work area (12) with the work implement (44), with anoperating width overlap (OL) between adjacent paths (P1, P2), to obtain apresent planned route (RP) comprises setting the operating width overlap (OL) based on terrain information in a stored map.

8. The method according to any of the preceding claims, wherein the present planned route (RP) comprises said at least a portion of the work area (12)being covered by a set of parallel paths (P1, P2) oriented in a first direction.

9. The method according to any of the preceding claims, further comprising comparing the deviation (D; DA; DM) of the estimated actual route (RA)from the present planned route (RP) to a previously stored deviation of aprevious estimated actual route from a previous route plan (RPO), the previousroute plan being different from the present route plan (RP); and setting a next route (RP2) based on said comparison. 10_The method according to claims 8 and 9, wherein the previous route plan

10. (RPO) comprises said at least a portion of the work area (12) being covered bya set of parallel paths (P3, P4) oriented in a second direction different fromsaid first direction. 16

11.The method according to any of the preceding claims, wherein planning aroute comprises defining a route in a GNSS reference system; and navigatingthe work area (12) comprises receiving GNSS signals.

12.The method according to any of the preceding claims, wherein the updatedoperating width overlap (OL) is further based on an estimated accuracy ofpositioning information from the positioning device (34).

13.The method according to any of the preceding claims, wherein the workimplement (44) has a fixed operating width (W), and setting an operating widthoverlap (OL) comprises setting a centre-to-centre distance S betweenadjacent paths (P1, P2).

14.The method according to any of the preceding claims, wherein the robotic tool(14) is a robotic garden tool.

15.The method according to claim 14, wherein the robotic garden tool (14) is arobotic lawnmower, the work implement (44) is a grass cutter, the operatingwidth (W) is a cutting width, and the task is cutting grass.

16.A method of navigating a self-propelled robotic tool (14) to perform a task within a work area (12), the method comprising navigating the work area (12) according to a present route plan (RP)while performing the task; recording an estimated actual route (RA) based on positioninginformation from a positioning device (34); estimating a deviation (D; DA; DM) of the estimated actual route (RA)from the route plan (RP); comparing the deviation (D; DA; DM) to a previously stored deviationfrom a previous route plan (RPO), the previous route plan (RPO) being differentfrom the present route plan (RP); and setting a next route plan (RP2) based on said comparison. 17.A method of navigating a self-propelled robotic tool (14) to perform a taskwithin a work area (12), the robotic tool (14) comprising a positioning device(34) and a work implement (44) having an operating width (W), the methodcomprising 17 planning a route to cover the work area (12) with the work implement(44), with an operating width overlap (OL) between adjacent paths (P1, P2), toobtain a present planned route (RP); navigating the work area (12) according to the present planned route(RP) while performing the task; determining an estimated actual route (RA) based on positioninginformation from the positioning device (34); estimating, for a path (P1), a deviation (D; DA; DM) of the estimatedactual route (RA) from the present planned route (RP); based on the deviation (D; DA; DM), determining that the path (P1) is afailed path; and updating the present planned route with at least one supplementary path(P1', P1") adjacent to the failed path (P1). 18.A self-propelled robotic tool (14) comprising a positioning device (34), a work implement (44) configured to carry out a task in a work area (12), andprocessing equipment configured to carry out the method according to any ofthe preceding claims. 19.A computer program product comprising instructions which, when the program is executed on a processor (26), carries out the method according to any of the claims1-17. 20.A computer-readable medium (98) comprising executable code representing instructions to a self-propelled robotic tool (14) to perform the method according to any of the claims 1-

17. 18